Legal heterodoxy is often assumed to entail a commitment to legal pluralism. Sunni legal theory represents an exception to this assumption. In the Sunni context legal heterodoxy represents an attempt to create a legal theory that generates univocal outcomes and rejects the legal pluralism endorsed by a majority of Sunni theories of the law. The most important and interesting critic of the emerging “orthodox” theory of law among Sunnis during the formative period of uṣūl al-fiqh (4th-6th Islamic centuries/10th-13th common era) was the Andalusian polymath, Ibn Ḥazm. In this essay I review the structure of Sunnī legal orthodoxy, and Ibn Ḥazm’s critique of that orthodoxy. I argue that the defining feature of Ibn Ḥazm’s theory of the law is not, as some have suggested, its limited application as compared to orthodox theories of the law, but rather his absolutist commitment to procedural integrity, and his rejection of any departure from pre-established rules of interpretation on substantive grounds.